High-intensity arc lamp for continuous operation



H. J. FREY March 26, 1957 HIGH-INTENSITY ARC LAMP FOR CONTINUOUS OPERATION Filed March 23, 1953 mm? MW United States PatentO HIGH-INTENSITY ARC LAMP FOR CONTINUOUS OPERATION Hans Jakob Frey, Zollikerberg, Zurich, Switzerland, assignor to Edgar Gretener, Zurich, Switzerland The present invention relates to high-intensity arc lamps, particularly to blown-arc lamps for continuous operation.

In the arc lamps generally employed today replacement of carbon electrodes requires interruption of the arc current and thus of light generation. This is highly undesirable in particular cases of application, e. g. with searchlights, or cinema and television projectors.

Arc lamps have become known wherein the individual electrodes have mating ends which fit into each other in order to permit continuous operation, additionally a binding paste may be applied .to these ends which is hardened by the heat of the arc in order to obtain a better mechanical and electrical connection of the individual electrodes. This will avoid disintegration. of the electrodes when the separation gap enters into the arc, and an uninterrupted transmission of the are current across this gap is to be avsaass Patented Mar. 26, 1957 'ice ' The electrodes employed in such a lamp for continuous operation are schematically shown by Fig. 2. With high intensity are lamps they customarily are composed of a pure-carbon shell and a core which has an admixture of metal salts. To permit continuous operation, shell 20 and core 21 of the individual electrodes are displaced relatively to each other, so that on one side the core issues as plug 22, whereas on the other side a socket 23 is formed by the shell. The carbon electrodes thus have mating ends which fit into each other. These ends are covered with a binding paste which may be fused and rendered electrically conductive by heating.

if the lamp shown by Fig. 1 is fed with such carbon electrodes they are fused within the oven 8. As a consequence the arc is fed with what may be called a practically homogeneous electrode of infinite length. This requires a suitable choice of the binding paste and a sufliciently achieved. Experience, however, has shown that by these means fluctuations or interruptions of light generation may not be avoided with absolute security.

The present invention has the object to overcome these difiiculties and is related to a high-intensity are lamp for continuous operation .by employment of carbon electrodes, the mating ends of which may be inserted into each other and are covered with an electrically ,cQnduC- tive binding paste fusible by heating. According to the present invention such a lamp is characterized by a heating device immediately disposed behind the electrode holder which elfects fusing of the attached electrodes before they enter into the holder.

The present invention will now be explained with the aid of the attached drawing, wherein:

Fig. 1 schematically .shows an embodiment of the Prescnt invention in perspective representation, and

Fig. 2 shows partly in a section the carbon electrodes employed in such a lamp.

In the lamp represented asembodirnent of the invention by Fig. 1 the are 1 is struck between the positive electrode 2 and the negative electrode 3. The crater 4 at the tip of the positive electrode represents the light source proper and is located in the focal point of the optical system, by ways of example of a concave mirror 5, which concentrates the light generated by the arc in a suitable manner, by ways of example in order ,to illuminate the aperture of a projector. The positive carbon 2 is supported in a holder 6 the positive head, which also contains the contacts, mostly brushes, for admitting the arc current, and is advanced by transport rolls 7 in the Well known manner as it burns away. Similar devices are provided for admitting current to an advancing the negative carbon 3, 'but which have not been shown in the drawing for the sake of clarity.

According to the present invention a heating device 8 is disposed immediately behind the electrode support, i. e. behind the positive head 6. This device may by ways of example be given the form of an electrically heated oven through which the electrodes pass on their way to the positive head.

high temperature Within oven 8.

By fusing the electrodes before they enter into the holder, soiling of the current brushes by binding paste or combustion products thereof is avoided. Furthermore the employment of a separate oven permit to establish fusing of the electrodes under most advantageous conditions as the duration of heating and the temperature may be adapted to any requirements. if necessary the temperature may also be varied according to the predetermined program in correspondence with the advance of the separation gap. All this cannot be effected within the hitherto known lamps as in these lamps fusing is efiected by the heat of the arc itself.

in the device according to the present invention fusing is furthermore effected before the carbon passes the current contact, e. g. a brush disposed on the electrode holder. This avoids contact disturbances caused by the formation of gas or drops. This may be brought about by evaporation or sweating out of the paste during g H Additionally a scraping device may be provided which removes remnants of the paste issued from the gap during fusing before the'carbori enters into holder 6. Such a scraping device 16 has schematically been shown in Fig. 1.

The present invention offers particular advantages if a blown-arc'lamp is employed, wherein an arcstream issuing from the positive holder concentricallysurrounds the positive electrodes. This are stream has approximately the form of a'hollow cone conver'gingin direction towards the negative electrode. Thereby the arc discharge and the anode tail flame are aligned and concentrated into the cylindrical space in front of the positive crater. This is schematically indicated in Fig. 1 wherein the positive holder additionally acts as air nozzle, having a ring shaped opening 9, from which a concentrical air stream 10 issues. An exhaust funnel 11 is provided on the negative side, which removes the arc stream and the flame gases. The air may be supplied to nozzle 9 as shown in Figure 3 of U. S. Patent No. 2,662,991 to Gretener, there being a common owner of the patent and this application.

With such are lamps as is Well known, extremely high current densities and correspondingly high light intensition of the present invention with a blown-arc therefore represents an extremely advantageous solution of high reliability of operation, as the electrodes fused by the heater device are not subject to mechanical stress. In contrast thereto, as is well known, other high-load highintensity are lamps require continuous rotation of the carbons in order to guarantee uniform consumption. The devices habitually employed for rotating the carbons exert high compression and torsion stresses, so that breaking of the fused gap may easily occur, and will cause interruption of operation.

As has been shown in Fig. 1, the heater device is preferably located within the shadow cone cast by the electrode holder 6, so that it does not cause additional disturbing shadows within the light beam reflected by mirror 5.

An arc lamp according to the present invention may also be constructed in such a manner that transport and insertion of carbon electrodes is effected automatically from a magazine. This is schematically shown in Fig. 1. A magazine 12 filled with new electrodes 13 is located at the rear of the positive electrode holder. The electrodes are urged upwards by a spring 14. The uppermost electrode is shifted into the opening of oven 8 by transport rolls 15. The speed of transport by rolls 15 is slightly higher than of rolls 7, so that fusing of the electrodes Within oven is effected under a certain pres sure. Rolls 15 by ways of example are driven through a slip clutch in order to avoid excessive wear of the advancing carbons. If the uppermost electrode has been transported so far that it issues from the magazine, the next electrode takes its place under the action of spring 14 and insertion of the ends is eifected by rolls 15.

Preferably the carbons are employed in the position shown in Fig. l, i. e. plug 22 forms the rear end of the preceding carbon, whereas socket 23 is located at the forepart of the succeeding carbon. Preferably a sufficient amount 24 of the binding paste is deposited within socket 23. By way of example, however, the socket 23 filled with paste may also be closed by a suitable cap 26 which is only pierced and thus opened when the carbon is inserted. Thereby soiling by leaking paste may be avoided during transport storage or in the magazine.

It may also be useful to provide lateral holes 25 in the socket 23. Through these holes excess of paste and its evaporation and combustion products generated during fusing may escape. If that is not possible bursting of the shell by the gases confined within the socket may occur.

As has been shown in Fig. 1 magazine and additional feeding means are also located within the shadow cone of the electrode holder, so that additional shadows are avoided.

In the preceding description means for continuous operation have been shown on the positive side. As has already been mentioned this offers particular advantages with lamps of highest current densities and correspondingly elevated consumption, which would entail inadmissibly short consumption periods of the individual electrodes with regard to the limitation of the length of the individual carbons imposed by the optical system.

The principle of the present invention may also beemployed on the negative side. With regard to the considerably lower consumption of the negative electrode this will in general not be necessary, particularly if the rod-shaped electrode is replaced by a disk-shaped electrode, the arc terminating on the disk edge.

Lamps with disk-shaped electrodes which have become known attain a manifold period of operation in comparison with rod electrodes, due to the uniform distribution of consumption along the entire edge of the disk.

I claim:

1. In a high-intensity arc lamp for continuous operation achieved by the employment of carbon electrodes with mating ends which may be inserted into each other and which are covered with a binding paste conductively fusible by heating, an electrode holder for supporting the positive electrode and a heater device immediately dis posed at the rear of said electrode holder which effects fusing of the electrodes inserted into each other before the separation gap enters into the arc.

2. In a high-intensity arc lamp for continuous operation achieved by the employment of carbon electrodes with mating ends which may be inserted into each other and Which are covered with a binding paste conductively fusible by heating, an electrode holder for supporting the positive electrode and a heater device immediately disposed at the rear of said electrode holder which effects fusing of the electrodes inserted into each other before the separation gap enters into the arc, said electrode holder having an air nozzle by which an air stream is directed towards the arc and surrounding the are as a hollow converging cone, whereby the arc discharge and are flame are concentrated into the cylindrical space in front of the positive crater.

3. In a high-intensity arc lamp for continuous operation achieved by the employment of carbon electrodes with mating ends which may be inserted into each other and which are covered with a binding paste conductively fusible by heating an electrode holder for supporting the positive electrode and a heater device immediately dispose at the rear of said electrode holder which effects fusing of the electrodes inserted into each other before the separation gap enters into the arc, said heater device being located within the shadow cone cast by the electrode holder, whereby additional shadows are avoided.

4. In a high-intensity arc lamp for continuous operation achieved by the employment of carbon electrodes with mating ends which maybe inserted into each other and which are covered with a binding paste conductively fusible by heating an electrode holder for supporting the positive electrode and a heater device immediately disposed at the rear of said electrode holder which effects fusing of the electrodes inserted into each other before theseparation gap enters into the arc, and a scraping device located in between the heater and the electrode holder for removing remnants of paste left after fusing.

5. In a high-intensity arc lamp for continuous operation achieved by the employment of carbon electrodes with mating ends which may be inserted into each other and which are covered with a binding paste conductively fusible by heating, an electrode holder for supporting the positive electrode and a heater device disposed immediately at the rear ofsaid electrode holder which effects fusing of the electrodes inserted into each other before the separation gap enters intothe arc, a magazine for new electrodes and additional transport means which effect automatic transport and insertion of the carbon clec trodes from the magazine.

References Cited in the file of this patent UNITED STATES PATENTS 1,785,587 Kuhlmann. Dec. 16, 1930 2,120,243 Droll June 14, 1938 2,657,326 McCarthy Oct. 27, 1953 2,662,991 Gretener Dec. 15, 1953 

